The invention generally relates to the generation of cryogenic cooling of materials by liquefied natural gas (LNG) for purposes of recycling and, more particularly, to the application of cryogenic cooling to the cryogenic grinding of scrap tires.
Most of the 270 million scrap tires produced in the U.S. are disposed of in landfills, converted to fuel, or recycled by shredding. Of these methods, cryogenic grinding and ambient wet attrition provide the highest resale value for the tire""s components and are the environmentally superior solutions by allowing for the creation of new products from these materials. These methods currently are used on less than 1% of the scrapped tires.
The traditional method of using liquid nitrogen to cool the tires to below xe2x88x92200xc2x0 F. adds approximately $0.40-0.60 in processing costs per tire. Recently, the use of air cooled to xe2x88x92202xc2x0 F. by means of an on-site cryogenic air cooler has been claimed to have reduced refrigeration costs to $0.20 to $0.60 per tire. The wet attrition grinding method avoids the processing costs associated with the consumption of liquid nitrogen or refrigerated air, but is energy intensive and requires much specialized equipment that is expensive to buy and to maintain.
The invention provides, in a preferred embodiment, a method for embrittling a material, including rubber. The material transfers heat to liquefied natural gas, vaporizing at least a portion of the liquefied natural gas and producing subsequently recovered natural gas in the process. Processes for transferring heat from the material to the liquefied natural gas include to the liquefied natural gas by direct contact, to a refrigerant that subsequently transfers heat to liquefied natural gas, and to a second refrigerant such as nitrogen that transfers heat to a first refrigerant that next transfers heat to liquefied natural gas.
A further embodiment describes a method for converting rubber in tires into rubber crumb and includes shredding tires, transferring heat from the shredded tires to liquefied natural gas, crushing the cooled, shredded tires, and separating the crushed, shredded tires into components that include rubber crumb. The method can include further cooling the rubber crumb, grinding the cooled rubber crumb into a ground product, and sorting the ground product into constituents such as fiber, steel, and rubber crumb. Crushing may be accomplished in a hammer mill and grinding in a grinding mill. Processes for transferring heat from the shredded tires and from the rubber crumb to the liquefied natural gas include to the liquefied natural gas by direct contact and to a second refrigerant such as nitrogen that transfers heat to a first refrigerant that next transfers heat to liquefied natural gas.
In yet another embodiment, an electrical conductor is cooled to a superconducting transition temperature by providing liquefied natural gas, transferring heat from the electrical conductor to the liquefied natural gas, vaporizing at least a portion of the liquefied natural gas in the process, and recovering the natural gas. Processes for transferring heat from the electrical conductor to the liquefied natural gas include to the liquefied natural gas by direct contact, to a refrigerant such as nitrogen that subsequently transfers heat to liquefied natural gas, and to a second refrigerant such as nitrogen that transfers heat to a first refrigerant that next transfers heat to liquefied natural gas.
In still yet another embodiment, a system is provided for the grinding of an elastomeric material where there is a supply of liquefied natural gas, a heat exchanger for transferring heat from the material to the liquefied natural gas so as to create cryogenically glassified material, a mill for grinding the cryogenically glassified material into ground material, and a transporter for removing the ground material. The heat exchanger can comprise a container to which liquefied natural gas is added and from which natural gas is removed and to which material is added and from which cooled material is removed. In addition, the heat exchanger can comprise a pipe into which the material enters at one end and from which cooled material leaves at the other end and a jacket surrounding the pipe having an input into which liquefied natural gas enters and an output from which a combination of liquefied natural gas and natural gas is extracted.